Graphite-free titanium carbide and method of making same



Patented Dec. 13, 1949 GRAPHITE-FREE TITANIUIW CARBIDE AND METHOD OF MAKING SANEE Charles C. Laughlin and Eugene Wainer, Niagara Falls, N. Y., assignors, by mesne assignments, to National Lead Company, New York, N. 'Y., a corporation of New Jersey No Drawing. Application July 23, 1945, Serial No. 606,706

2 Claims. 1

The present invention relates to the prepara tion of a new titanium carbide of superior hardness and more particularly to a graphite free titanium carbide containing a small amount of chromium.

Commercial titanium carbide as presently manufactured has anumber of major uses in view of its great hardness. It is used as an ingredient of high speed cutting tools usually in combination with tungsten carbide but sometimes in its absence; as a base for electrical contact points; as an ingredient of heat-resisting compositions, and others.

The present process for producing titanium carbide involves heating a mixture of titanium oxide and carbon to 1800 C. or higher. The product obtained invariably contains several percent of free carbon in the form of graphite. The presence of free graphite in amounts over 0.2% sharply reduces the utility of the product, the hardness is reduced and the product disintegrates readily on application of heat. When used as a contact point, unequal electrical and thermal stresses are developed leading to disintegration. In general, rather involved procedures are required to eliminate the free carbon, which procedures are generally costly and, as often as not, unsuccessful in operation.

In order to obtain any benefit from the use of titanium carbide in a cutting tool, the free carbon must be reduced below 0.2%, such a product being called a graphite-free titanium carbide in the trade. Such a graphite-free product imparts the necessary toughness, hardness, and durability to the finished product required for utility, whereas the graphite-containing product, especially if it contains one to three percent of graphite, as it usually does, is practically useless or of very limited utility in these respects.

It is an object of the present invention to prepare titanium carbide as an initial reaction product which meets the specification of a graphitefree product, that is, a product in which the graphite content is negligibly low.

It is also an object of the invention to include in the reaction mixture employed to manufacture titanium carbide a material which will eliminate graphite from the mixture at the temperature of operation.

It is also an object of the invention to make unnecessary the after treatments presently employed to reduce the free carbon or graphite of titanium carbide to manufacture the so-called graphite-free product of commerce.

It is also an object of the invention to prepare a titanium carbide having a small predetermined amount of chromium .therein and a product of superior hardness, toughness and durability as compared with graphite free titanium carbide prepared by elutriation procedures.

The novel product of the present invention is prepared by heating a mixture of titanium oxide and carbon of the approximately proper stoichio metric proportions to produce titanium carbide and, the addition, to the mixture of a small amount of chromium oxide. The temperatures of the reaction are in the range 3600 F. to 4000 F.

The general equationtfor the formation of titanium carbide is as follows:

TiO2+3CSTiC+2CO However, free graphite is always present.

This free graphite is obtained in three ways:

1. By reversal of the reaction which reversal takes place readily.

2. By performing the reaction at too high a temperature. Under these conditions, TiC dissolves carbon very readily which, oncooling, precipitates as graphite. The temperatures of active formation and fusion of TiC are so close together it is practically impossible to prevent this solution of carbon. This is the most important source of free graphite.

3. An incomplete reaction due to improper time temperature relations.

We have found that the addition of chromium oxide or compounds of chromium to the reaction mixture of titanium oxide and carbon has'a peculiar and highly beneficial effect. Apparently, chromium compounds form complexes with carbon which are at least partially volatile at the temperature of rapid formation of titanium carbide. If the process be carried out in a closed container, a sublimate is obtained on the cooler portions of the receptacle consisting chiefly of chromium carbide. In view of the boiling out of the free carbon as a chromium complex at reaction temperatures, the most important source of free graphite is automatically eliminated with respect to the titanium derivative. A portion of the chromium, however, always remains behind.

The titanium carbide so produced and containing the residual chromium is superior to ordinary graphite-free titanium carbide in a number of respects. It is much tougher and harder. A sintered bar of the chrome-titanium-carbide will scratch a bar made of ordinary graphite-free titanium carbide. The color is silver white as against silver grey. The crystals of titanium carbide are large and well formed. As long as sufiicient chromium is present, the stabilizing action due to volatility of the chromium-carbon complex is effective. In addition, the presence 4 rapidly as possible and then raised to 4000 F. in 30 minutes with the production of excellent grades of titanium-chromium car-bide of great hardness and ductility in those instances where the added of chromium reduces or eliminates the reversible 5 chromium in the mix was sufficient to reduce the reaction which is a secondary source of free free carbon to below 0.2%.

r phi Finally, h th rd s ur of graph- The rutile used in the examples listed in the i m y in mp t a t n, may be ntable contained 96% T102 and 0.34 Cr2O3. The ated y p p attention to time temperature 7 total CrzOs content in the raw batch was the relations. 10 sum of the amount added and that present in the In the practice of the invention, we may rutile. It will be understood that the examples use as raw material in the charge either na- 'are merely illustrative and not limitative of the tural rutile or brookite or, where extreme purinvention.

Reaction Mixtures Theoretical Final Products I #Reactm 'g. g. in and 3 'liC i ggf gig i Per Cent Rutile Coke OM03 formed Carbon Carbon Cr O;

809 362 nil m1 78.7 18.82 1.05 1111 309 362 nil 0. 47 0. 97 0.15 309 362 6.0 1. 48 78.3 18.28 0.11 0.88 162 72 2. 4 2. 40 76. 5 1s. 31 0. 06 1. 44 324 145 9.6 4.40 76.3 17.58 0.04 3.21 162 72 7. 2 6. 46 75. 4 17.13 0. 0s 3. 67 162 72 9.6 8.51 76. 0 17.23 0. 05 3. 22 162 72 12.0 10. 42 76.1 16. 90 0.08 s. 19 162 72 14. 5 12. 62 72. 5 18.30 0.11 5. 61

ity is required, We may use the chemically pre- We have found that at least 0.6% CrzOs and pared titanium oxide of commerce. For all pracpreferably 1.0% CrzOs by weight, based on the tical purposes, natural rutile is eminently suit- TiC to be formed, should be present in the raw able, particularly since modern methods of benemix to compensate for that lost in the reaction fication allow the preparation of rutiles of to obtain the beneficial results. high T102 content. From a free carbon standpoint, the beneficial If rutile containing chromium as an impureffects of the use of the proper amount of ity be available, it may be effectively used in 3 chromium is evident by comparison of reactions 1 the practice of the invention by addition of sufand 2 with reactions 3 to 9 The final product ficient chromium compound to bring the chroshould contain at least a few tenths of a percent mium content of the reaction mix up to the of CrzOs and may contain up ,to several percent, amount required to eliminate the free carbon. the effect on elimination of free carbon being For the purposes of our invention, the rutile clearly evident when the raw batch contains an is preferably ground to a fineness of about -325 amount of CI203 equivalent to about 1.5% of the mesh. As the source of carbon we prefer to use TiC finally formed. In the absence of sufficient any low ash, low volatile type coke. This may be chromium as a constituent of the reaction mixelectric furnace carbon or calcined pitch coke, or ture the free carbon elimination is erratic and calcined petroleum coke. uncontrollable.

While chromium oxide is preferably employed Itappears from reaction #3 that the raw batch in the reaction mix, a number of chromium coms o d o t t least 1.0% Cr203 as a safe oppounds are satisfactory for our purposes such as c ating minimum, since 0.6% ClzOa was lost and the ammonium or alkali chromates and substannce about 0.4% CrzOs should be retained. As tially any chromium compound not adversely af 50 appears from the table, last column, a content of fecting the properties of the titanium carbide about 3% of 01203 in the final product, TiC, remay be employed. The simplest and most suitable suits in minimum free'carbon content. material is the green pigment grade chromium From'the above, it will be seen that a procedure oxide of commerce. 7 is provided whereby, as an initial product, a ti- In the practice of our invention, we generally tanium carbide of graphite-free quality can be grind the ingredients together in a ball mill so prepared provided the reaction batch of titanium that the ultimate particle size is such as to pass a oxide and carbon contains sufiicient chromium 325 mesh screen. The dry, well mixed batch is to eliminate the graphite formed. The amount of then rammed into a graphite shell and the batch chromium should be sufficient to provide a quanheated to a temperature range of 3600l0l0 F. tity remaining in the final titanium carbide to so that this temperature range is maintained provide control over free carbon formations and throughout the batch for at least 30 minutes but for removal of a portion thereof as volatile not over about 45 minutes,:these times and temchromium'carbide. While we have indicated that peratures being such as to engender the formaabout 1.0% 0 :203. in the 'IiC is effective deparn. tion of TiC. e ap Shell Completely entures from this figure may be made and are concloses the reaction except for. a' small hole at the templated within the invention. top to permit the escape of gases. After the re- Wh t is claimed action is complete, the source of heat is removed 1. h g a f gnanufa ctuying t t and the gas vent closed off to prevent oxidation. bi e ccntaining less than 92% graphite which After cooling, the product is milled in an iron ball comprises providin mixture Consisting of t mill to 325 mesh and. the slip treated with acid t m-um dioxid and carbon in approximately to remove iron, f y p W2-Shed with stoichiometric proportions for titanium carbide water and the product dried. reaction, and a compound of chromium existing In the following ex p es, the batches w as the oxide and i'oriningcarbide at the reaction made up as indicated and ed o 3 as temperature, said chromium compound being present in sufiicient amount to form volatile chromium carbide with graphite formed in the titanium carbide and to provide a chromium content calculated as 0.88% to 3.67% CrzOz, based on the titanium carbide reaction product, and firing said mixture to a reaction temperature of 3600 F. to 4000 F., whereby the titanium carbide produced contains less than 0.2% graphite, and chromium calculated as 0.88% to 3.67% Cr2O3.

2. Tough, hard and highly refractory titanium carbide containing graphite in an amount less than 0.2% and chromium, calculated as 0.88% to 3.67% Cr2O3, based on the titanium carbide.

CHARLES C. LAUGHLIN. EUGENE WAINER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,119,489 Beer May 31, 1938 2,173,749 Boecker et a1 Sept. 19, 1939 FOREIGN PATENTS Number Country Date 478,016 Great Britain 1938 

